Viscoelastic properties of dilute macromolecular solutions can provide information about molecular size, shape, and flexibility. The Birnboim-Schrag multiple-lumped resonator will be used to study, at very low concentrations, biomacromolecules such as light meromyosin, F-actin, shear-degraded DNA, helical polyaminoacids (especially in the vicinity of the helix-coil transition), and xanthan polysaccharide. From the frequency dependence of the storage and loss shear moduli, the flexural rigidity of such a rodlike molecule can be deduced, as well as the relaxation time associated with end-over-end rotation. From similar measurements on suspensions of shell-like structures such as retinal rod outer segment disc membranes, the elasticity of the confining membrane can in principle be deduced. The kinetics of ligation of fibrin oligomers will be studied by a combination of polyacrylamide and agarose gel electrophoresis, under conditions where only gamma-gamma or both gamma-gamma and alpha-alpha ligation occur, and with modified as well as native fibrinogens. Mechanical properties of fibrin clots, both fine and coarse (i.e., without and with substantial lateral aggregation or protofibrils) and both ligated and unligated, will be studied by measurements of creep and creep recovery. In large deformations, the differential dynamic modulus can be measured simultaneously by a special torsion pendulum apparatus to follow structural damage and reconstitution during creep and recovery. Gels of other proteins and polyaminoacids may also be studied. Mechanical properties of fibrin film, which has a much higher fibrin concentration, will be studied by stress relaxation and creep and correlated with measurements of small-angle and wide-angle X-ray scattering, optical rotatory dispersion, and electron microscopy to elucidate the molecular mechanisms for high extensibility and recovery from deformation.